The prior art describes a variety of grafts that are used for the replacement of diseased passageways in a living body. In addition, the prior art teaches several metallic reinforcements used for stenting to hold open constricted passageways in a living body. Moreover, there exists in the prior art stent-grafts which are generally a combination of these two separate components which are commonly used to repair aneurismal vessels.
The prior art includes grafts manufactured of materials such a textiles, polytetrafluoroethylene, expanded polytetrafluoroethylene, platinum, and gold. Due to the limitations of the materials employed, these prior art grafts have relatively large wall thicknesses that limit the bore size in cylindrical embodiments which results in a restriction or a pressure drop as contents such as blood flow through the graft. The heavy wall thickness also increases the possibility of the living body rejecting the foreign graft. Furthermore, the prior art expanded polytetrafluoroethylene materials have inferior physical properties such as strength and abrasion resistance which are important properties for safe installation and providing long service life. In particular, the prior art grafts offer significant room for improvement in suture retention and tear resistance. These prior art grafts also require the use of a separate component to hold open the bore of cylindrical shaped grafts. Exemplary patents of grafts include: U.S. Pat. No. 6,025,044 to Campbell (2000); U.S. Pat. No. 6,038,484 to House (2000); and U.S. Pat. No. 6,517,571 to Brauker (2003). Exemplary patents for producing expanded polytetrafluoroethylene include: U.S. Pat. No. 3,953,566 to Gore (1976); U.S. Pat. No. 3,962,153 to Gore (1976); U.S. Pat. No. 4,096,227 to Gore (1978); and U.S. Pat. No. 4,197,390 to Gore (1980).
The prior art reinforcements used for stenting are typically manufactured completely of materials such as stainless steel, tantalum, and nickel-titanium alloys. These stents are usually transported to the location of installation in a reduced size where they are subsequently dilated to come into contact with the interior surface of the passageway in which they are being installed. Despite attempts to make stents more flexible through the use of a large variety of configurations, the reinforcements used for stenting made of these prior art materials are sometimes difficult to install in small or curved passageways. In addition, due to size limitations a surgeon normally needs over two stents on average to complete a stenting procedure. Furthermore, the reinforcements used for stenting are generally of the uniform thickness from first end to second end which creates a stress concentration at the notch between the passageway in which it is installed and the end of the stent. This stress concentration can result in failure of fragile passageways such as human arteries or veins. Exemplary patents of metallic reinforcements used for stenting include: U.S. Pat. No. 4,739,762 to Palmaz (1988); U.S. Pat. No. 5,102,417 to Palmaz (1992); U.S. Pat. No. 5,449,373 to Pinchasik (1995); U.S. Pat. No. 5,972,018 to Israel (1999); and U.S. Pat. No. 6,884,260 to Kugler (2005).
In the prior art there are also grafts and stents which include bioactive materials. Coated medical devices have experienced problems with the coating flaking off or causing the recipient to have an allergic reaction when in-vivo. Pathologists have also found that drug eluting metallic stents have problems with delayed healing so that the endothelial layer of cells that would normally cover the members of the stent was non-existent or uneven thereby resulting in thrombosis which resulted in patient death. It was unexpected that the present invention provides potential for a more consistent and even growth of the endothelial layer of cells by providing a more accurate and controlled release of active ingredients over time.
The prior art drug eluting stents also require a longer term antiplatelet therapy than bare metal stents. Since the surfaces of the bare metal stents are thrombogenic, the drug eluting stents are designed to inhibit or slow cell growth in an attempt to eliminate restenosis. The active ingredients included in the drug eluting stents, however, require that the patients be given an antiplatelet therapy for a longer period of time while the artery heals and a thin layer of endothelial cells grows over the members of the stent to reduce the risk of thrombus. Due to this phenomenon the Federal Drug Administration (FDA) recommends that the period of therapy be increased from 6 weeks for bare metal stents to 3-6 months for use with drug eluting stents and in some cases doctors prescribe some medications for longer periods of time such as for life. This therapy adds substantial daily expense for the patient and in many cases the patients are allergic to the medications and they cause the patients to have unwanted side effects like illness and a higher risk of uncontrolled bleeding during future surgical procedures.
There is also a significant problem of attaching active ingredients to the prior art medical devices like grafts and stent-grafts that have polymeric surfaces. It was surprising how significant of an improvement of adhesion of active ingredients and coatings could be achieved to the medical devices comprised of polymers in the present invention by including additives in the polymers. This improvement was especially noticeable when the additives partially or fully protruded from the surface of the polymer because the additives appear to mechanically lock the active ingredients, coating, or combinations thereof to the polymeric surface.
The prior art drug delivery mechanisms also can also provide the patient with imprecise drug dosage and modified release characteristics especially when employed over long periods of time. For drug eluting stents the imprecision of the dosage is related to the difficulty of evenly dispersing active ingredients in coatings, obtaining a uniform dry coating film on partially vertical surfaces like those found on stents, and inconsistent delivery related to poor adhesion of coating to the stent's surface. Furthermore, for a graft the imprecision is primarily related to the heterogeneous structure of the prior art materials like found in expanded polytetrafluoroethylene and the poor adhesion to polymeric surfaces. The highly uniform structure of the expanded material of the present invention and the improved adhesion enables a significant improvement in the precision of active ingredient delivery over time. Moreover, the active ingredients showed potential to significantly improve patency by positioning the active ingredients between layers of expanded material instead of on the surface or in coatings on surface.
Due to the high shear stress that develops during bending of a stent-graft while sliding it through the torturous path of the human anatomy, there is a significant risk in the prior art stent-grafts that the graft will tear at the connection points between the stent and graft. This risk is increased as the wall thickness of the graft is reduced. It is highly beneficial to patient safety to increase the graft wall strength and to minimize the wall thickness of the graft to minimize pressure drop through the graft and to enable the use of grafts in smaller sizes. If the graft separates from the stent there is risk the graft will collapse causing a restriction in flow or worse yet a life threatening leak. In the prior art there are attempts to reduce tearing by modifying the mechanical design of the connections but this often results in a larger than necessary wall thickness that causes unnecessary restrictions in flow or lack of flexibility of the stent-graft. In the present invention, there are tear arresting additives which enable thinner wall thicknesses without tearing regardless of mechanical design.
The large wall thicknesses of the prior art grafts comprised of expanded polytetrafluoroethylene employ paste extrusion techniques using relatively large particle size raw materials. The fine powder polytetrafluoroethylene [PTFE] of the prior art such as Asahi Glass Co. Fluon® CD-123 has an average particle size of about 475 microns, Asahi Glass Co. Fluon® CD-1 has an average particle size of about 550 microns, Dupont 601A has an average particle size of about 570 microns, and Dupont 610A has an average particle size of about 470 microns. It was surprising to discover in the present invention that potential exists for thinner wall thicknesses by using smaller particle size polytetrafluoroethylene raw materials. Moreover, these wall thicknesses could be substantially more durable and have increased adhesion characteristics by including additives and nano size articles.
The present invention addresses the aforementioned limitations of the prior art by providing: a novel material that is suitable for use in a prosthesis deployed in a living body that is incrementally expandable from a first size to a second size through deformation or self-expansion; a prosthesis that is substantially more flexible and capable of conforming to the natural curvatures of passageways in a living body when installed using, for example, noninvasive surgery techniques such as those employing a catheter or a balloon catheter; a prosthesis that can have a variable wall thickness to reduce creating a stress concentration between the prosthesis and the passageway in which it is installed, a prosthesis that has minimal drag against the interior wall of a passageway in a body when inserted through the passageway; a prosthesis material and manufacturing process that enables the production of very small sizes and a large variety of sizes so that surgeons can, for example, repair very small blood vessels and use less prostheses per procedure; a prosthesis having a relatively thin wall thickness that substantially increases the size of the bore in tubular embodiments increasing flow and reducing pressure drop; a prosthesis that is self-expanding from a first size to a second size that undergoes relaxation to manage the outward radial pressure applied to a supporting passageway such as blood carrying artery, a prosthesis that more accurately delivers the dosage of active ingredients like drugs with or without a coating especially over long periods of time; a prosthesis that includes surface treatments, additives, or combinations thereof that substantially minimizes the risk of coatings or active ingredients from flaking-off the surface of the prosthesis and can sometimes assist in maintaining the original position of the prosthesis after deployment, and a prosthesis that can include biological cells grown in vivo or vitro that can be implanted into a body as, for example, a blood carrying vessel or organ to replace unrepairable portions of the anatomy.